From c74e29b714a1ee0cd73faddea57426b311d24d2e Mon Sep 17 00:00:00 2001 From: Henry Fricke Date: Mon, 3 Aug 2026 20:29:32 -0600 Subject: [PATCH] Verify GNU Parallel doc on live Easley, fix stale imagemagick note and broken example Ran every example in this doc live on Easley. The "imagemagick module unavailable" callout was stale (dated ~June 23, promised a fix "within a day") - module load imagemagick works fine now, so removed the callout. Also found the file-conversion example itself was broken independent of that: ImageMagick's convert can't turn .csv into .txt, it only understands image formats. Replaced it with a real png->jpg conversion example and tested it. Also verified: gzip/gunzip compression, single-node MATLAB+parallel (4 CSVs produced), the --sshloginfile passwordless-SSH-between-nodes setup, and both the 2-node matlab_parallel.slurm and python_parallel.slurm batch scripts - confirmed via GNU Parallel's joblog (task start times and hostnames) that these genuinely run distributed across both allocated nodes rather than silently falling back to one node. Co-Authored-By: Claude Sonnet 5 --- GNU Parallel.md | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/GNU Parallel.md b/GNU Parallel.md index 5fd9c15..154dae1 100644 --- a/GNU Parallel.md +++ b/GNU Parallel.md @@ -20,25 +20,27 @@ Typical use cases include: ### Converting Files in Parallel -> **Known issue:** the `imagemagick` module is currently unavailable on Easley. A fix is expected within a day — until then, skip this example. - -The following example converts all `.csv` files into `.txt` files. +The following example converts all `.png` files in the current directory into `.jpg` files, using ImageMagick's `convert` for the actual per-file conversion and GNU Parallel to run many conversions at once. ```bash module load parallel module load imagemagick -find . -name "*.csv" | parallel convert {} {.}.txt +find . -name "*.png" | parallel convert {} {.}.jpg ``` This command: -1. Finds all files ending in `.csv` +1. Finds all files ending in `.png` 2. Passes each file to GNU Parallel 3. Executes conversions concurrently `{}` represents the full filename and `{.}` removes the extension. +Note: ImageMagick's `convert` only understands image formats — it can't be used to turn arbitrary files like `.csv` into `.txt`. For converting non-image data between formats in parallel, replace `convert {} {.}.jpg` with whatever conversion command is appropriate for your file type (e.g. a script or a different CLI tool); GNU Parallel itself doesn't care what command it's fanning out. + +`convert` prints a one-time deprecation warning in this version of ImageMagick (IMv7) suggesting `magick` instead — both work identically here, but `magick {} {.}.jpg` is the more future-proof spelling if you're starting fresh. + --- ### Compressing and Decompressing Files @@ -358,4 +360,4 @@ sbatch python_parallel.slurm --- -*This QuickByte was updated and validated on June 23, 2026.* +*This QuickByte was updated and validated on August 3, 2026.*